Growing Sea Kale in Scotland: The Complete Guide

Crambe maritima

Sea kale suits the Scottish climate: it's native to British coasts and rated H7The RHS's H1a–H7 scale for how much cold a plant can survive outdoors, H1a being tender indoor-only and H7 hardy anywhere in the UK. Full definition →, hardy below -20°C. What it asks for is patience and a technique rather than shelter from the cold.

This is a long-lived coastal perennial, not a leafy annual despite the shared "kale" name: a clump of large, wavy-edged blue-green leaves with a long tap rootA single, thick, dominant root growing straight down from a plant, storing energy and anchoring it, as opposed to a spreading mass of fine roots. Full definition → that resents being moved once planted. Grown mainly for its blanchedExcluding light from part of a growing plant, usually by earthing up, wrapping or covering, so it grows pale, tender and less bitter. Full definition → spring shoots, produced by excluding light from the crownThe base of a perennial plant where roots and shoots meet, often sold and planted as a ready-made dormant plant rather than grown from seed. Full definition → over winter, it rewards a slow start with spring shoots. Left uncovered to flower, it carries small, scented white flowers in summer that attract pollinating insects, an option if you'd rather grow one plant ornamentally than force it.

Perennial Vegetables Worth Growing in Scotland → compares sea kale against the other permanent-bed crops worth the same long-term commitment.

Planting

Plant a young pot-grown plant, or a root cutting known as a "thong", into its permanent position in early spring: choose the site carefully, since the long tap root makes established plants very difficult to move later. Root cuttings, taken from the side roots of older plants, are covered with about 2cm of compost. Seed is also an option, though the hard seed coat needs soaking and scoring before sowing in a cold frame in spring or autumn. Choose a sunny or lightly shaded site, ideally with fertile, very well-drained soil (it will tolerate poor soil) and enough depth and width for the tap root to spread; sea kale isn't suited to containers. It naturally occurs on shingle and sand on coasts, but it still needs shelter from strong winds, even on an exposed coastal plot. It tolerates acid, alkaline or neutral soil, so pH isn't a constraint, and it will tolerate poor soil and partial shade.

The first two years

Leave the plant alone through its first year to build a strong root system. Don't force any plant before its second year, as forcingCovering plants to exclude light and speed early, tender growth in the dark, most associated with rhubarb and sea kale in late winter. Full definition → weakens it. Cut the old growth down to ground level in autumn.

Varieties

Care

Add a thick mulchA layer of material spread over the soil around plants to suppress weeds, retain moisture, and improve soil structure as it breaks down. Full definition → of well-rotted manure or garden compost each spring. Beyond that, an established plant needs very little routine attention: water during extended dry spells, but otherwise this is a low-maintenance perennial once its site and root system are settled.

Blanching and harvesting

Over winter, cover the plant with a bucket or a rhubarb forcer to exclude light. This is what produces the pale, tender shoots sea kale is grown for. Cut the young shoots in spring, eaten raw or steamed, with a flavour close to asparagus. The young leaves are edible too, cooked as a vegetable, and young flowering shoots can be cooked like sprouting broccoli, so one plant gives three harvests.

Forcing Chicory, Sea Kale & Strawberries → covers the same blanching principle applied across all three crops, plus what it buys you in each case.

Common problems

• Slugs and snails are a problem on young shoots; netting or barriers help.
• Caterpillars can damage foliage, the same family of pests that troubles other brassicasThe cabbage family: cabbage, kale, broccoli, cauliflower, Brussels sprouts, kohlrabi, swede, turnip and more, sharing the same pests, diseases and rotation rules. Full definition →.
• Clubroot can affect sea kale, as it does other brassicas: avoid a site where cabbages, kale or other brassicas have grown recently.

Common questions

Sources